Texas Instruments ISO124U

Overview

ISO124U from Texas Instruments is a precision analog isolation amplifier with galvanic isolation across a 2-pF differential capacitive barrier, designed for high-voltage industrial signal conditioning. It delivers ±10-V bipolar output, 0.010% maximum nonlinearity, 50-kHz small-signal bandwidth, and 140-dB isolation mode rejection at 60 Hz - used in thermocouple isolation, 4–20 mA loop interfaces, and motor control feedback circuits.

For engineers reviewing the ISO124U datasheet, ISO124U pinout, ISO124U application, or ISO124U equivalent, key selection considerations include its fixed unity-gain configuration, dual ±4.5 V to ±18 V supply operation, 1500-Vrms rated isolation, and requirement for separate high-side/low-side ground references (Gnd 1 and Gnd 2) to maintain signal integrity in ground-loop-critical systems.

Technical Context

The ISO124U employs duty-cycle modulation-demodulation: the input voltage is converted to a 500-kHz square wave with variable duty cycle, transmitted digitally across two embedded 1-pF capacitors, then reconstructed as an analog output. Its modulator integrates VIN/200 kΩ against a switched ±100-µA current source, while the demodulator uses sense amplifiers and sample-and-hold stages to suppress ripple and deliver precise unity gain.

No external components are required for basic operation. The device contains 250 transistors, laser-trimmed for matching between input and output sections. It operates in a single functional mode with no user-configurable states, and exhibits aliasing behavior above 250 kHz due to its sampling-based architecture - requiring anti-alias filtering for wideband inputs.

Key Specifications

Pinout & Package

ISO124U is supplied in a 16-pin PDIP package (17.90 mm × 7.50 mm), with dual isolated supply domains and dedicated ground references per side.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision isolation amplifier applications.

Compared with ISO124U, ISO122U offers superior DC accuracy but sacrifices bandwidth, while AMC1301DWVR shifts to digital isolation with higher speed but requires firmware-level integration - neither is pin-compatible, and both demand PCB and schematic revisions for substitution.

Availability

ISO124U is available at Aetrix Electronics and suitable for industrial process control, motor control feedback, and battery management systems requiring stable component supply across extended product lifecycles.

Supply support for ISO124U includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of expertise in high-reliability isolation solutions.

The ISO124U belongs to TI's precision isolation amplifier product line, engineered specifically for industrial signal conditioning where galvanic separation, low drift, and high linearity are mandatory - targeting applications in factory automation, energy infrastructure, and test equipment.

FAQ

What is the maximum input voltage the ISO124U can safely handle?

The ISO124U supports a continuous analog input voltage range of ±10 V, with absolute maximum rating of ±12.5 V. Exceeding ±10 V violates recommended operating conditions and risks nonlinearity increase beyond 0.010% FSR. Input protection is not integrated - external clamping or scaling is required for overvoltage scenarios. The ISO124U datasheet specifies ±10 V as full-scale for guaranteed performance.

Does the ISO124U require external components for basic operation?

No, the ISO124U operates in fixed unity-gain configuration with no external resistors or capacitors required for core functionality. However, 1-µF tantalum bypass capacitors on each supply pin (+VS1, –VS1, +VS2, –VS2) are mandatory per the datasheet to stabilize the 500-kHz internal oscillator and suppress supply noise. Output ripple filtering is optional but recommended for noise-sensitive applications.

Can the ISO124U be used with single-supply operation on the high-voltage side?

Yes - the ISO124U supports single-supply operation on the high-voltage side using a Zener diode (e.g., 5.1 V) to generate the –VS1 rail, as documented in Figure 21 of the ISO124U datasheet. Input range becomes asymmetric (e.g., –2 V to +10 V), but the ISO124U maintains full ±10 V output swing because the low-side section remains dual-supplied. This configuration is validated for industrial sensor interfaces.

What is the purpose of having two separate ground pins (Gnd 1 and Gnd 2) on the ISO124U?

Gnd 1 serves as the return reference for the high-side input section (VIN, +VS1, –VS1), while Gnd 2 is the return for the low-side output section (VOUT, +VS2, –VS2). These grounds must remain physically and electrically isolated to preserve the 1500-Vrms galvanic barrier. Connecting them defeats isolation and invalidates safety ratings - proper PCB layout requires split ground planes separated by ≥8 mm creepage/clearance.

How does the ISO124U handle high-frequency common-mode transients?

The ISO124U achieves high-frequency transient immunity through digital duty-cycle modulation: the analog signal is converted to a 500-kHz square wave before crossing the capacitive barrier, making it insensitive to barrier impedance variations. Its isolation mode rejection remains >80 dB up to 100 kHz, and false triggering is avoided below 1000 V/µs dV/dt - verified by TI's partial discharge testing at 2400 Vrms.